Filter media

ABSTRACT

Improved air filters of felt carrying electrically charged resinous particles comprise a felt made from a mixture of wool and acrylic fibers.

Umted States Patent 11 1 1111 3,850,600 Monsted, Jr. Nov. 26, 1974 [5 FILTER MEDIA 2,573,964 11/1951 Green et a1. 55/524 2,670,305 2 1954 W' [75] Inventor: Mlmsled, Glenshaw, 3,251,475 5?]966 T11? 55/527 [73] Assignee: Mine Safety Appliances Company,

Pittsburgh, Pa. Primary Examiner-Bernard Nozick Filed: y 1973 Attorney, Agent, or Firm-Ronald H. Shakely, Esq.

21 App]. No.: 376,429

52 us. 01. 55/524, 55/528 [57] ABSTRACT [51] Int. Cl 801d 39/16 [58] Field 01 Search 55/524, 522, 527, 528; Improved air filters of felt. y g electrically 210/5Q3 5()5, 50 50g 509 charged resinous particles comprise a felt made from a mixture of wool and acrylic fibers. [56] References Cited UNITED STATES PATENTS 4 Claims, N0 Drawings 2,514,145 7/1950 Stevens 55/524 FILTER MEDIA BACKGROUND OF THE INVENTION Wiswesser, US. Pat. No. 2,670,305. The resinous matcrial may be incorporated by mixing powdered resin with the fibers and then felting the mixture. Or a preformed felt may be impregnated with a solution of the resinous material, dried, and then mechanically worked to break up the resin into small particles. The mechani cal working creates an electrical charge in the resin particles that is retained for a long period of time; To the best of my knowledge, only wool felts have been used in making filters of this type, although the patents mention felts containing small amounts of cotton, other plant or animal fibers, or other fibers.

DESCRIPTION OF THE This invention is based on our discovery that felted filter media carrying electrically charged resinous par ticles in which the felt is a mixture of wool and acrylic fibers has unexpectedly improved efficiency against dust and improved retention of efficiency in the presence of charge degrading conditions, such as exposureto humidity or oil smokes.

Felts are non-woven textiles in which the fibers are interlocked by suitable mechanical work, such as needling. The felts used in this invention are made from a mixture of wool and acrylic fiber, the proportions of which do not appear to be critical so long as there is an effective minimum amount of the minor fiber, suitably a significant proportion of at least about l percent by weight. Under present economic conditions it is preferred that the major fiber component be acrylic and the minor fiber component be wool.

resinous materials disclosed in the earlier mentioned patents. Such frangible or brittle'resins will take'an electrical charge when mechanically broken into small particles. The proportion of the resin is not critical and filters having from about 2 percent to 50 percent weight resin are practical for use for various purposes; 15 percent percent resin is now generally preferred .for respirators to provide a favorable balance between filtering efficiency and resistance to air flow through the filter.

The following examples are illustrative of this invention.

Example 1. An I 1 02. felt, .010 inches thick, was im mersed in a 7.5 percent solution of zinc resinate in trichloroethane solvent and the excess solution was removed by passing the felt through squeeze rolls. The

impregnated felt was oven dried and then worked by' running it between grooved rollers to give a filter containing about 20 percent by weight of resin. Filters so prepared, using felts containing various proportions of wool (grade 608 to 70S) and acrylic fiber (Orlon 39,'

2.5 denier, textile length) were subjected to the DOP test, a standard test for measuring filtering efficiency of oil smokes. DOP, dioetyl phthalate, is vaporized into an air stream forming an oil smoke of highly uniform small particle size, on the order of 0.3 u, and drawn through the filter to be tested. The percentage of DOP penetrating throughthe filter is measured, the higher percent- Acrylic fibers are manufactured fibers in which the fiber-forming substance is any long chain synthetic polymer compound of at least 85 percent by weight acr eilit e 1 9 (ii l gum, calcium resinate and polystyrene, as well as other age penetration representing poorer filter efficiency. The results set out in Table 1 demonstrate the exceptional increase in filtering efficiency and resistance to degradation of filtering efficiency when using filters with felts of mixed wool and acrylic fibers.

Table I Time Exposed 7c DOP Filter Felt to DOP Smoke Smoke Penetration 5 Seconds 20 I00% Wool 5 Minutes 63 5 Seconds 0.2 50% Wool 25 Minutes 10 50% Acrylic 79 Minutes 82 5 Seconds 0.3 30% Wool 23 Minutes 10 Acrylic 88 Minutes 63 Example II. Filters made as in the previous example, and exposed to air at l00F and percent relative humidity for time periods up to 21 days were subjected to the standard silica dust test for measuring filtering efficiency for submicron particles; the higher leakage representing lower efficiency. From the test results set out in Table II it will be observed that a percent acrylic felt filter is much less efficient than a 100 percent wool felt filter and that mixed fiber filters have a filtering efficiency about an order of magnitude greater than those of wool or acrylic fiber. After one day aging in a charge degrading atmosphere the efficiency of the wool v felt filter was drastically decreased, making it practically useless as a respirator filter. The mixed-fiber filters, on the other hand, retain a high efficiency even after prolonged exposure to the same atmosphere of at least 21 days and for an indeterminate longer period.

Table II Number of Days Silica dust test leakage, mg. at lF., 50% acrylic 70% acrylic 80% RH. l00% wool 50% wool 30% wool 100% acrylic Not aged 1.3 mg. 0.l mg. 0.1 mg. 22 mg.

1 day 6.7 mg 0.1 mg 0 1 mg 8 days 0.1 mg. 0.1 mg. 2] days 0.5 mg. 0 2 mg.

(ligaximfm allowed according to Bureau of Mines Respirator Test Schedule 1. mg.

It will b recognized that y inv ntion can be pracand the retention of dust collection efficiency under ticed otherwise than as specifically described herein 15 charge degrading conditions. and that the invention iS based on my discovery Of the 2, A filter according to claim 1 having a felt contain- ?expecmd, synelglsnc ,effect of acryhc'wool ing a minor proportion of one fiber in an amount of at I claim: least about percent by weight. 1. A filter of felted-fibers carrying mechanically elec- 2O 3. A filter according to claim 1 having a felt containtrified resin particles in which the felt consists essening a major proportion of acrylic fiber. tially of wool fibers and acrylic fibers, each fiber being 4. A filter according to claim 1 having zinc resinate present in an amount at least about 10 percent by particles. weight effective to improve dust collection efficiency fl 3'. fl

a-.. a a-c I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,850,600 Dated November 26, 1974 Inventor(s) John W. Monsted, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 13, .010" should read 0.10 Column 3, following line 1?, insert mixed fiber felts in resin carrying felt filters.

Signed and sealed this 29th day of April 1975.

(SEAL) Attest: C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks FORM PC4050 uscoMM-Dc seam-ps9 "-5. GOVERNMENT PRINTING OFFICE 2 199 0-365-33 

1. A FILTER OF FELTED FIBERS CARRYING MECHANICALLY ELECTRIFIED RESIN PARTAICLES IN WHICH THE FELT CONSISTS ESSENTIALLY OF WOOL FIBERS AND ACRYLIC FIBERS EACH FIBER BEING PRESENT IN AN AMOUNT AT LEAST ABOUT 10 PERCENT BY WEIGHT EFFECTIVE TO IMPROVE DUST COLLECTION EFFCIENCY AND THE RETENTION OF DUST COLLECTION EFFICIENCY UNDER CHARGE DEGRADING CONDITIONS.
 2. A filter according to claim 1 having a felt containing a minor proportion of one fiber in an amount of at least about 10 percent by weight.
 3. A filter according to claim 1 having a felt containing a major proportion of acrylic fiber.
 4. A filter according to claim 1 having zinc resinate particles. 